In general, the lower layer dependence of a TEOS (tetraethyl ortho-silicate)-O.sub.3 oxidizing film is influenced by the content of ozone (O.sub.3). To improve the lower layer dependence, the ozone concentration should be suitably adjusted, i.e. a plurality of TEOS-O.sub.3 layers should be formed with different ozone concentrations. In other words, it is intended to improve the lower layer dependence and evenness by adjusting the ozone concentration of the TEOS-O.sub.3 whereby the layer deposited first has the lowest O.sub.3 concentration which is gradually increased in the later deposited TEOS-O.sub.3 layers. The "lower layer dependence" of TEOS-O.sub.3 film means that the TEOS-O.sub.3 film has differences in thicknesses and in quality (density) according to the characteristics of the layers formed on its lower portion. For example, when an oxidation film is formed on the substrate and a poly pattern is formed on a predetermined portion of the oxidation film, if TEOS-O.sub.3 is formed on both the oxidation film and the poly pattern, the thickness and the quality (density) of the TEOS-O.sub.3 film on the oxidation film are different from that of the TEOS-O.sub.3 film formed on the poly pattern. In other words, the TEOS-O.sub.3 film is hydrophilic and so is the oxidation film, whereas the poly pattern is hydrophobic. Thus, the TEOS-O.sub.3 film has a better characteristic of deposition over the poly pattern rather than over the oxidation film.
A conventional TEOS-O.sub.3 oxidizing film depositing system is described with reference to FIG. 1.
FIG. 1 is a block diagram of a conventional TEOS-O.sub.3 oxidizing film depositing system.
As can be shown in FIG. 1, the conventional TEOS-O.sub.3 oxidizing film depositing system comprises an ozone generating zone 2 which generates ozone from oxygen introduced through a suitable adjusting Mass Flow Controller (MFC) zone 1 and a Mass Flow Controller (MFC) zone 2 which controls the amplitude of the flow. A chamber 3 is provided where the depositing of the TEOS-O.sub.3 oxidizing film on a wafer takes place by introducing oxygen and ozone generated in the ozone generating zone 2 as well as a silicon source through opening 3b into the chamber.
The chamber comprises a first inlet opening 3b for introducing the silicon source and depositing the TEOS-O.sub.3 oxidizing film on a wafer substrate 3a. A second inlet opening 3c is provided for introducing ozone having a finally adjusted concentration into the chamber. Dispersion head 3d disperses the silicon source and ozone introduced through the first and second inlet openings 3b and 3c on the wafer 3a. A heater 3e is operatively associated with the wafer 3a.
The TEOS-O.sub.3 oxidizing film depositing system suitably adjusts the output of the ozone concentration from the ozone generating zone (2) to form a TEOS-O.sub.3 oxidizing film layer. The ozone is formed, for example, by the UV radiation of air or oxygen and its concentration can be varied by adjusting the amount of current applied to the UV lamp. The ozone concentration of the oxidizing film layer which is first deposited on the wafer 3a is reduced if the flow of oxygen from the Mass Flow Controller zone 1 increases. Upon gradually reducing the oxygen inflow, the ozone concentration increases accordingly.
However, the conventional TEOS-O.sub.3 oxidizing film depositing system described above has the following disadvantages.
First, a long time is required for the ozone concentration to reach a stabilized state, and this shortens the life span of the UV lamp.
Second, if the TEOS-O.sub.3 oxidizing film is deposited by using very low ozone concentration in order to remove lower layer dependence due to high ozone concentration, the evenness will deteriorate.